The method relates to a method for actuating an electromagnetic load which can be switched between at least two switching states, in particular a magnetic valve, wherein switching between a first and a second of the switching states takes place as a result of a current flowing through the load by means of applying an electrical voltage to said load.
Methods and devices for actuating an electromagnetic load which can be switched between at least two switching states, in particular a magnetic valve, are known from the German patent publication DE 4 341 797 A1 as well as from the European patent publication EP 0 764 238 B1. A voltage is applied to an electromagnetic load in the methods and devices described there. The current flowing through the load increases on account of the applied voltage. This first increase in current, referred to below as current ramp-up, continues up until the current flowing through the electrical load achieves a predetermined threshold value. The current ramp-up ends upon achieving the threshold value, and the current flowing through said load is controlled to a nominal value via an open-loop or closed-loop control device, preferably by clocking the voltage—ie. by periodically applying and not applying said voltage. A switching of the electromagnetic load from a first to a second of the switching states always takes place after said current ramp-up. When switching between states, magnetic parts or parts connected to them, as, for example, an armature or a valve needle, move on account of the current flowing through said load from on position to another. The positions correspond, for example, to end positions, particularly to a rest or operating position. The movement of the magnetic parts causes a characteristic change in the profile of the current, provided a magnetic circuit of the electromagnetic load interacting with said parts has not gone to saturation. The current profile during the current control is evaluated to determine the point in time of the switching process, and the switching point in time of the electromagnetic load is determined with the help of the temporal profile of the current. The electromagnetic load actuated in this manner can, for example, be a magnetic valve, which is primarily used to control the injection of fuel, for example, into an internal combustion engine. The point in time of the switching process, whereat the moving, magnetic parts of the electromagnetic load achieve in each case one of their two end positions, is particularly of interest for the exact metering of the smallest injected quantities.
The known systems take the approach—as previously described—that the current is clocked after the current ramp-up and is thus controlled to a nominal value. The switching process of the electromagnetic load always occurs during this nominal value control after the current ramp-up. For this reason, a change in the current profile, which is not based on the control but on the switching of the electromagnetic load is always evaluated in this phase as the point in time of the switching process. Following said switching process, the voltage applied to the electromagnetic load continues to be clocked so long as the switching state of the electromagnetic load is to be maintained. In this method, it is always necessary to ensure that the switching of the electromagnetic load does not already occur during the current ramp-up but particularly in the phase of the current control. A circuit for implementing the method must therefore likewise be laid out accordingly. Method and circuit must consequently be adapted to the prevailing conditions, as, for example, applied voltage and parameters of the electromagnetic load, which is why they are not universally applicable.